Cook lights in slightly salted water till tender, then take them out of the stock; when cooled, cut into thin strips.
Mix onions, garlic, bay leaf, gherkins, capers, parsley, thin lemon peel and thyme, and chop all into tiny pieces.
Fry the sugar in the melted lard until it is brown; add the flour, stir till dark brown.
Put in the mixed and chopped spices, stir and when they are partially fried, add the paprika; pour on the stock and, stirring with a whisk, boil the whole for 15 mins.
It must not be too thick or too thin.
Put in the sliced lights, add mustard, lemon juice and the amount of vinegar required, salt, and cook the whole for another 15 20 mins.
Place in a deep dish.